Part A4 United Buildings

It is not unusual for authorities to receive plans proposing the joining of two or more buildings. Joining of buildings could be achieved by breaking openings through walls, or by joining the buildings by a tunnel, bridge or covered walkway.

When joined, if the buildings jointly comply with all the requirements of the BCA applying as if they were a single building, they become a united building.

United buildings are not required to comply with additional BCA provisions. For example, any new openings do not require any form of fire protection not required of a single building.

Note, however, an external wall, which as a result of an interconnection becomes an internal wall, must comply with the requirements for an internal wall.

Interconnected buildings which do not jointly comply with all the requirements applicable to a single building, remain as separate buildings.

This raises the possible need for fire doors, or other forms of protection to be fitted to the new openings.

The BCA does not concern itself with actually prohibiting or permitting the uniting of buildings in separate ownership or on separate allotments. Such matters are dealt with by the relevant local bodies.

In this example, Building A is connected to Building B by bridge C. There are four different options for designing such a proposal.

The first is a united building

A, B and C are considered as a single structure and comply with the BCA.

The second is three separate buildings

A, B and C are a fire-source feature to each of the others, and are separated by fire walls with the openings protected at the points of connection. In this case, C may require independent support and separate egress to a road or open space, that is not through Buildings A or B. In this case, attention should also be paid to the length of the bridge, as regards distance of travel to an exit.

The third option is the bridge as a portion of Building A

In this option, A and C are one building, meeting all requirements of the BCA as a single or united building. B is a separate building, with suitable fire separation, including fire-doors at the point of interconnection. Bridge C could be supported off Building A, but not off Building B.

The fourth option is having the bridge as a portion of Building B

In this option, B and C are one building, meeting all requirements of the BCA as a single or united building. A is a separate building, with suitable fire separation, including fire doors at the point of interconnection. Bridge C could be supported off Building B, but not off Building A.

In some cases, C will link A and B across a public road, including laneways and the like. Special approvals may be required from various appropriate authorities. However, in such cases:

• if C is supported by means other than off A and B, such support will generally only be permitted if there is no obstruction of the public road;
• care will need to be taken in calculating the distance of travel to an exit if travel is required to be over C and the road is wide; and
• fire-separation may be necessary at each end of the bridge.

If the last stipulation is the case, the following matters need consideration:

• the bridge would probably need to be of fire-rated construction because combustible construction could provide a ready path for the transfer of fire, and non-combustible construction could, in a major fire, distort and collapse onto the road;
• the designer needs to take care that the bridge does not negate the fire separation between the storeys of the building.